Diamond-like carbon and oxide bilayer insulator for magnetoresistive transducers

ABSTRACT

A magnetic structure is formed by depositing a layer of diamond-like carbon onto the exposed surface of an a first material and depositing a layer of second material onto the layer of diamond-like carbon. A photoresist is applied to the exposed surface of the second layer and is patterned in the form of the desire structure. The exposed portions of the second layer are removed with a wet etchant that does not attack the diamond-like carbon layer. Thereafter, any remaining photoresist is removed.

This is a divisional of application Ser. No. 08/571,469, filed Dec. 13,1995.

BACKGROUND OF THE INVENTION

This invention is directed to a process for fabricating a thin filmmagnetic structure and the magnetic structure fabricated thereby.

Many magnetic transducers employ magnetic layers, or soft adjacentlayers (SALs), adjacent an insulating material. In inductive heads, theinsulating material might be used for a gap for the magnetic transducer.Typically, the insulating material is deposited first (such as onanother magnetic layer or on a substrate) and the magnetic layer ispatterned on top of the insulating layer. Typically, a photoresist ispatterned in the desired shape of the magnetic layer and a wet chemicaletchant is applied to the exposed portions of the magnetic layer toshape the magnetic layer into the desired pole. The etchant employed inremoving unwanted portions of the magnetic layer also often attacks thedesired insulating layer, resulting in a reduction of the thickness ofthe insulating layer and a compromise of the characteristics of thetransducer. There is, accordingly, a need for an etchant stop to protectthe insulating layer and to form a part of the resulting gap.

SUMMARY OF THE INVENTION

The present invention is directed to a magnetic structure having amagnetic layer and a layer of insulating material with a layer ofdiamond-like carbon sandwiched between the magnetic layer and theinsulating layer. In one form of the invention, the structure is amagnetic transducer that includes a second magnetic layer and theinsulating layer and layer of diamond-like carbon form a gap for thetransducer.

According to one aspect of the present invention, a layer ofdiamond-like carbon is deposited onto the exposed surface of aninsulating layer and a layer of magnetic material is deposited onto thelayer of diamond-like carbon. A photoresist is applied to the exposedsurface of the magnetic layer and is patterned to a desired shape. Theexposed portions of the magnetic layer are removed with a wet chemicaletchant that does not attack the diamond-like carbon layer. Thereafter,any remaining photoresist is removed. In one form of the invention, theinsulating layer is deposited onto a base magnetic layer, and theinsulating layer and layer of diamondlike carbon together form a gap fora magnetic transducer

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a section view taken at line 1—1 at FIG. 2, near the airbearing surface of a magnetic head in accordance with the presentinvention.

FIGS. 2A and 2B illustrate the process of forming the patterned magneticpole in accordance with the present invention.

FIGS. 3A and 3B illustrate the process of milling a soft adjacent layerin an MR head using diamond-like carbon as part of the insulatingunderlayer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, a magnetic structure includes a lower magnetic layer10, and upper magnetic layer 12 and a layer 14 of insulating oxide suchas silicon dioxide (SiO₂) or aluminum oxide (Al₂O₃). Layer 15 ofdiamond-like carbon is formed over layer 14. Layers 10 and 12 aretypically a nickel/iron metal alloy, such as Sendust or Permalloy. Layer12 may be a soft adjacent layer (SAL) for a magnetoresistive (MR) head(not shown) above layer 12, and layer 10 may be a bottom shield (withlayers 14 and 15 providing an insulating layer between them).Alternatively, layers 10 and 12 may be poles separated by a gap formedof layers 14 and 15, such as for a read or write head. In any case, thestructure employs a layer of insulating oxide material such as SiO₂ orAl₂O₃ below a to-be patterned layer of magnetic material However,pinholes are formed in deposited layers of SiO₂ and Al₂O₃.

Prior use of only insulating SiO₂ or Al₂O₃ layers over the magneticlayer did not always protect the magnetic layer from etching when themagnetoresistive layer was etched. More particularly, if the insulatinglayer was not adequately thick, i.e., greater than about 750 to 1000Angstroms, pinholes formed in the SiO₂ or Al₂O₃ layer allowed etchant topass through the layer and attack the magnetic layer below. The presentinvention applies a diamond-like carbon layer over the insulating layerto protect the insulating layer and lower magnetic layer duringsubsequent processing.

FIGS. 2A and 2B illustrate the process of forming the head structureshown in FIG. 1 in accordance with the presently preferred embodiment ofthe present invention. As shown in FIG. 2A, insulating layer 14 isdeposited over the top surface of magnetic layer 10. Typically, layer 14has a thickness of less than about 750 Angstroms, and therefore may havepinholes that could allow penetration of etchant. A layer ofdiamond-like carbon 15 is applied over layer 14, and magnetic layer 12is applied over layer 15. Layer 15 may be quite thin, about 200Angstroms being adequate in most cases. A layer of photoresist 20 isapplied over the entirety of layer 12 and is patterned as shown in FIG.2A to the desired shape of the SAL to be formed in layer 12. A wet acidetchant, such as one based on hydrochloric acid, is applied to theexposed portions of layer 12 to etch and remove the exposed portions oflayer 12.

Most insulating materials, such as SiO₂ and Al₂O₃, form pinholes whichpermit passage of etchant. At thicknesses less than about 750 Angstroms,such insulating materials are poor etchant stops. One characteristic ofdiamond-like carbon is that it is substantially free of pinholes, evenat thicknesses of about 200 Angstroms. Since the wet acid etchant doesnot attack the diamond-like carbon, the etchant cannot reach theinsulating layer 14. As a result, the SiO₂ or Al₂O₃ insulating layer 14is protected from the wet etchant by the diamond-like carbon layer 15which is not attacked by that etchant. Upon completion of the etching oflayer 12, the remaining photoresist 20 is dissolved, leaving thestructure illustrated in FIG. 2B and ready for encapsulation as shown inFIG. 1.

Diamond-like carbon is commercially known as “DLC” and is commerciallyavailable from a variety of sources. The diamond-like carbon is similarto diamond in physical properties. The material is a hydrogenated carbontypically having a hydrogen content between about 30 to 50 percent and alarge fraction of sp³ carbon-carbon bonds rather than sp² found inordinary graphite. The material is typically formed from a hydrogenatedcarbon feedstock, such as methane (CH₄), processed by any of a varietyof processes, such as an ion beam deposition process. It is theorizedthat during formation of diamond-like carbon, hydrogen is removed fromthe feedstock material forming a network of SP³ bonded carbon atoms,rather than an ordered array of Sp² bonded carbon, i.e. graphite. Thematerial resembles a hard, highly cross-linked polymer and exhibits ahigher thermal conductivity than common electrical insulating material(such as SiO₂ or Al₂O₃) and a high electrical resistivity, of the orderof about 10¹⁰ Ω-cm. Diamond-like carbon films are similar to-diamonds inthat they exhibit very high hardness ranges (1,000 to 5,000 on theVickers hardness scale), a low coefficient of friction (of the order ofless than 0.1) and densities between about 1.7 and 2.2. The material iscommercially referred to as “diamond-like” because of its similarity incharacteristics to natural and synthetic diamond. Moreover, like naturaland synthetic diamond, the diamond-like carbon exhibits a highresistivity.

Diamond-like carbon is a good electrical insulator, although it is alsohighly thermally conductive. Hence, diamond-like carbon layer 15 formspart of the insulating or gap layer and provides dissipation of heatfrom the resulting head. Another advantage of the diamond-like carbonlayer is that the layer is not susceptible to attack by the etchantsused to etch the oxide layer, so the integrity of the oxide layer ismaintained. Moreover, etchants ordinarily used in subsequent processingof the head do not attack diamond-like carbon. Thus, wet etchants usedin shaping Ni/Fe magnetic films do not attack the diamond-like carbonetchant stop layer. As a result, the head is less susceptible ofdelamination during subsequent processing.

FIGS. 3A and 3B illustrate the use of a diamond-like carbon layer tocontrol ion milling where the diamond-like carbon is left in thetransducer as part of the insulating layer. FIG. 3A illustrates an MRhead having a metal reader bottom shield 60 and an insulating layer 62on layer 60. Insulating layer 62 is an insulating oxide, such as Al₂O₃or SiO₂. A layer 64 of diamond-like carbon is deposited over layer 62,and a soft adjacent layer (SAL) 66 is formed over layer 64. A layer 68of tantalum is formed over SAL 66, and a layer 70 of magnetic materialforms the magnetoresistive element. Conductive layers 72 and 74 areformed of a cobalt-platinum alloy and provide electrical connectionbetween gold or copper contacts 76 or 78 and opposite sides of MRelement 70. Optionally, an additional insulating layer may be formedbetween SAL 66 and layer 68 to form a free SAL FIG. 3B illustrates theprocess of patterning SAL 66.

As shown in FIG. 3B, the magnetic material to form the SAL 66 isdeposited on the top surface of the diamond-like carbon layer 64. Alayer of photoresist 80 is formed on SAL layer 66 and patterned into theshape of the SAL The exposed portions of the photoresist layer 80 andSAL layer 66 are then ion milled to remove most photoresist and to millto a depth at least equal to the thickness of SAL layer 66. Thephotoresist and SAL layer have approximately the same mill rate.However, the diamond-like carbon has a mill rate one-fifth that of theSAL Consequently, there is very little milling into the insulating layerformed of layer 62 and diamond-like carbon layer 64, thereby resultingin a well formed SAL fully patterned by ion milling without significantmilling into the underlayer insulation. After the milling is completed,any remaining photoresist is exposed, dissolved and washed away.Moreover, since the diamond-like carbon is itself a good insulator, itmay remain as part of the underlayer.

One feature of the invention is the fact that the diamond-like carbon isapplied by an ion beam deposition directly onto layer 14 or 64. Thesimplicity of the ion beam process permits the formation of low defectfilms in the diamond-like carbon. Other techniques for applying thediamond-like carbon to layer 14 or 64 include radio frequency and directcurrent magnetron sputtering, carbon-arc deposition, laser ablation, andplasma enhanced chemical vapor deposition (PECVD).

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. A magnetoresistive transducer having amagnetoresistive layer, a first magnetic layer forming a soft adjacentlayer operatively associated with the magnetoresistive layer, a secondmagnetic layer forming a magnetic shield for the transducer, and anelectrical insulator sandwiched between the first and second magneticlayers, characterized in that the electrical insulator contains a layerof insulating oxide material adjacent one of the first and secondmagnetic layers and a layer of thermally conductive, high electricalresistivity diamond-like carbon adjacent the other of the first andsecond magnetic layers.
 2. The magnetic transducer of claim 1 where thelayer of insulating oxide material is SiO₂.
 3. In a magnetoresistivetransducer having a magnetoresistive layer, a magnetic soft adjacentlayer operatively associated with the magnetoresistive layer, and amagnetic shield layer forming a magnetic shield for the transducer, theimprovement comprising insulating means sandwiched between the magneticshield layer and the soft adjacent layer for electrically insulating thesoft adjacent layer from the shield layer and for conducting heat fromthe transducer, the insulating means comprising a layer of insulatingoxide material and a layer of thermally conductive, high electricalresistivity diamond-like carbon.
 4. The magnetic transducer of claim 3where the layer of insulating oxide material and the layer ofdiamond-like carbon are contiguous.
 5. The magnetic transducer of claim4 where the layer of insulating oxide material is SiO₂.
 6. The magnetictransducer of claim 3 where the layer of insulating oxide material isSiO₂.